ESTIMATIONS OF THE AGGREGATION TIME OF VARIOUS COLLOIDAL SYSTEMS

Scaling approximations for the time after which macroscopic aggregation becomes visible are derived for various colloidal systems. It is shown that the aggregation rate, which is generally used as a measure of stability, is not the only factor determining the aggregation time. The total number of bonds that have to be formed before aggregation becomes visible is at least as important. The aggregation rate increases abruptly when orthokinetic aggregation or sedimentation becomes dominant or just before gelation occurs. This enables the estimation of an aggregation time without the use of an arbitrary or operational definition of visibility. This aggregation time refers to macroscopic aggregation, e.g. visible sedimentation or gelation. Complications that hinder an accurate determination of the aggregation time are listed, and their effects on the aggregation time are predicted. The obtained scaling relations provide useful insights into the progress and results of colloidal aggregation phenomena.